Product Overview

The Allen-Bradley 1785-L20E is a high-performance central processing unit (CPU) within the classic PLC-5® family, specifically engineered for integrated Ethernet communication. This single-slot controller module resides in a 1771 I/O chassis, providing powerful logic processing for medium-scale industrial automation. The "E" designation signifies built-in Ethernet capabilities, allowing the processor to communicate across factory networks without the need for additional bridge modules.

As a cornerstone of the 1771 platform, the 1785-L20E is designed for long-term reliability in manufacturing environments. It manages up to 512 total I/O points across multiple local and remote racks. The processor is optimized for tasks ranging from simple discrete logic to complex analog processing, floating-point math, and high-speed data handling, ensuring seamless operation for legacy system maintenance or localized expansion.

Technical Characteristics

• Memory Capacity: 16,000 (16K) words of user-available SRAM.

• Ethernet Connectivity: Integrated 10/100 Mbps port supporting EtherNet/IP for peer-to-peer messaging and SCADA interfacing.

• Built-in Protocols: Includes one dedicated Data Highway Plus (DH+) port and one universal DH+/Remote I/O port.

• Serial Interface: Supports RS-232, RS-422A, and RS-423 standard communication.

• I/O Capacity: Controls up to 512 I/O (any mix of inputs and outputs) with support for up to 12 remote I/O racks.

• Data Backup: Primary memory is protected by a 1770-XYC Lithium battery; supports 1785-ME series EEPROM modules for non-volatile storage.

• Processing Speed: Rapid scan times as low as 0.5 ms per KB of logic; I/O scan rate of 3ms at 230.4 kbps.

• Chassis Compatibility: Installs in 1771-A1B, -A2B, -A3B, -A3B1, or -A4B universal I/O chassis.

• Physical Specifications: 4.8 x 15 x 27.3 cm; Weight: 1.18 kg.

• Industrial Hardening: Rated for 30G operational shock and 1G vibration resistance.

Network Integration and Scalability

The 1785-L20E excels in bridging traditional factory floor networks with enterprise-level Ethernet. By supporting DH+ and Ethernet concurrently, it allows for easy data collection and programming over high-speed links while maintaining robust control over legacy Remote I/O (RIO) drops. This dual-network capability is vital for facilities looking to modernize their data visibility without replacing entire banks of field-side wiring.

Programming is conducted via RSLogix 5, providing a familiar environment for ladder logic development. The module includes a high-accuracy real-time clock and calendar, essential for time-stamping alarms and coordinating batch processes. To ensure maximum uptime, the controller features comprehensive self-diagnostics that monitor hardware health, battery status, and network integrity. Whether serving as a standalone controller or a node in a massive distributed network, the 1785-L20E remains a reliable workhorse for the industrial sector.